In response to regulations implemented by the United States government, automotive manufacturers are starting to provide new vehicles with tire pressure monitor/monitoring (TPM) equipment. Initiated in the year 2000, Congress passed the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, which related to issues concerned with the operation of a vehicle with substantially under-inflated tires. Under-inflated tires can result in a tire separation/blowout, which adds to the potential for a loss of control of a vehicle. Additionally, under-inflated tires shorten tire life and increase fuel consumption.
Section 12 of the TREAD Act directed the Department of Transportation (DOT) to complete a rule requiring that new motor vehicles must include a warning system that indicates if tires are under-inflated. Ever further, in response to Section 12 of the TREAD Act, the National Highway Traffic Safety Administration's (NHTSA) National Center for Statistics and Analysis (NCSA) conducted the Tire Pressure Special Study (TPSS), which was designed to assess to what extent passenger vehicle operators are aware of the recommend tire pressures for their vehicles, the frequency and the means they use to measure their tire pressure, and how significantly the actual measured tire pressure differs from the manufacturers recommend tire pressure.
As a result of the TPSS, NHTSA favored a direct system using monitors in each wheel to determine whether tires are properly inflated so as to alert drivers when tire pressure is low. In early 2002, NHTSA issued a regulation mandating the implementation of TPM systems in new vehicles beginning with the 2004 model year. Under that rule, TPMs had to warn motorists when tire pressure fell 25% or 30% below the vehicle manufacturer's recommended level. The new standard applies to passenger cars, trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle.
TPMs have been implemented in two ways: using the vehicle's antilock brake sensors in an indirect approach, or, by installing TPM sensors inside the tires prior to inflation on the wheel rim in a direct approach. Although the cost of the direct approach is higher than that of the indirect approach, it is preferred due to its precision and reliability. In a conventional operating environment, the signals transmitted from sensors inside tires to a receiving antenna often exhibit poor reception characteristics due to an interaction of the signals with the vehicle body, road, nearby vehicles, other nearby objects, and the like. The poor reception characteristics of the antenna often result in the triggering of a failure mode for the microprocessor unit.
In most cases, the receiving antenna is typically a remote keyless entry (RKE) antenna that receives signals from all of the vehicle's tires, which is then subsequently passed to a microprocessor for information processing. The RKE antenna is traditionally chosen for TPM due to its frequency range and relatively low cost and easy installation characteristics. Because the RKE antenna is a single antenna that is typically installed on one of the side windows or back-windshield glass, the RKE antenna alone may not be sufficient for some situations to receive the tire pressure signals propagated through an electromagnetically harsh environment, which has, for some applications, effected the reception capability of the most distant tire pressure sensor relative the position of the RKE receiving antenna.
These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail.